Characteristics and causes of complications after internal fixation of femoral neck fractures based on OTA/AO classification / 中华创伤杂志

ABSTRACT

Objective:To investigate the characteristics of complications after internal fixation with hallo nails for femoral neck fractures according to OTA/AO classification and analyze the reasons for differences in complications of different classifications based on the current theories and lever-fulcrum balance theory.Methods:A retrospective case series analysis was made on clinical data of 113 patients with femoral neck fractures treated in Peking University People's Hospital from January 2014 to June 2020. There were 49 males and 64 females, with the age of 21-89 years [61(52, 72)years]. According to OTA/AO classification, there were 5 patients with type B1.1 fractures, 18 with type B1.2, 16 with type B1.3, 44 with type B2.1, 5 with type B2.2, 12 with type B2.3 and 13 with type B3. All patients were treated by percutaneous internal fixation with hallo nails. Complications were recorded during follow-up including femoral head necrosis, nonunion, screw back-sliding and screw cut-out. Causes of internal fixation complications were analyzed based on the lever-fulcrum balance theory, taking the location of fulcrum, screw stress (F1), force arm of pressure (L1), resistance of screw (F2) and resistance side (L2) into consideration.Results:All patients were followed up for 1.1-77.5 months [8.2(3.6, 16.6)months]. In all, 24 patients had complications, including femoral head necrosis in 7 patients, nonunion in 3, screw back-sliding in 12 and screw cut-out in 2. The rate of femoral head necrosis of type B1, B2 and B3 was 15%(6/39), 2% (1/61) and 0%, respectively. The rate of femoral head necrosis of type B1 was higher than type B2 ( P<0.05). The nonunion rate was 3%(1/39) in type B1, 3%(2/61) in type B2, and 0% in type B3 ( P>0.05). The rate of screw back-sliding of type B1, B2 and B3 was 3%(1/39), 2%(1/61) and 0%, respectively. The rate of screw back-sliding of type B2.3 and B3 were higher than that of type B1 ( P<0.05). A trend toward a higher rate of screw back-sliding of type B2.3 and B3 was found when compared to type B2.1/2.2, but there was no significant difference ( P>0.05). Moreover, the rate of screw back-sliding showed no significant difference between type B2.3 and B3 ( P>0.05). The rate of screw cut-out was 3%(1/39) in type B1, 2%(1/61) in type B2, and 0% in type B3, which showed no significant difference between type B1 and B2 ( P>0.05). According to the lever-fulcrum balance theory, the extent of pathologic fulcrum of type B1, B2 and B3 gradually increased, resulting in increased L1 and decreased L2. The L1 of type B1, B2 and B3 was (2.2±0.5)cm, (2.8±0.4)cm and (4.7±0.5)cm, respectively ( P<0.01). The L2 of type B1, B2 and B3 was (5.1±0.5)cm, (4.7±0.5)cm, and (3.6±0.4)cm, respectively ( P<0.01). Therefore, the F1 of type B1, B2 and B3 increased progressively. Conclusions:After internal fixation, the rate of femoral head necrosis of type B1 is significantly higher than that of type B2, and the rate of screw back-sliding of type B1 is significantly lower than that of type B3. The lever-fulcrum balance theory can deepen our knowledge of reasons for complications after operation for femoral neck fractures.